I just put my Volant in two days ago and i love it!
build quality- 8
sound- 9 (by sound i mean the sound when you get on it, it made the exhaust sound alot deeper and throatier as far as it actually sucking in air i cant hear it from inside the cabin)
performance-8 (Throttle response is alot better and the power is WAAY noticeable)
installation-5 ( as anyone who puts one in will tell you the design team could have done better but it still fits good)
overall happiness and referral- 10 (I freaking love this thing! Defiantly would recommend it!
One thing that made me go with Volant is that its a closed box and a dry filter two big ++ IMO AND no maintenance for 100k miles, so they say.